An oil-and-gas industry group said the Environmental Protection Agency’s (EPA) water testing at a Wyoming natural gas drilling site raises concerns about the agency’s national study on hydraulic fracturing.

The American Petroleum Institute (API) warned Thursday that EPA’s testing practices in Pavillion, Wyo., used too small a sample size to determine whether hydraulic fracturing, or fracking, contributed to groundwater contamination. The group said that could have far-reaching implications for EPA’s national study on that linkage.

“If EPA thinks its investigation at Pavillion has produced scientifically useful information, then it may proceed in the same inexpert way at other testing sites, assume it is getting additional useful information, and employ that information to justify changes in public policy,” Erik Milito, API director of upstream, said.

Fracking injects a high-pressure mixture of water, chemicals and sand into tight rock formations to unlock hard-to-reach natural gas deposits.